MicroBGA printing problem

I've had some trouble pasting a test board for a MicroBGA trial. Most of the paste remains in the stencil apertures. The stencil is 6 mil thick, laser cut and electo-polished. The apertures are 12 mil in diameter with 20 mil pitch. We are using Alpha Metals WS-609 paste.

Any suggestions would be greatly appreciated.

Thanks, Doug

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| I've had some trouble pasting a test board for a MicroBGA trial. Most of the paste remains in the stencil apertures. | The stencil is 6 mil thick, laser cut and electo-polished. | The apertures are 12 mil in diameter with 20 mil pitch. | We are using Alpha Metals WS-609 paste. | | Any suggestions would be greatly appreciated. | | Thanks, | Doug | Much of the work we've done with 20 mil pitch devices is done with nearer 1:1 aperture to pad relationships. When using no-clean types, as you might be suggesting, the paste can be especially "sticky" requiring larger openings to effect required prints thus violating some reduction rules for other device types. Also, more frequent stencil cleaning, in the machine, is required - every two prints with wet, dry, vacuum programming, as an example.

Earl Moon

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| I've had some trouble pasting a test board for a MicroBGA trial. Most of the paste remains in the stencil apertures. | The stencil is 6 mil thick, laser cut and electo-polished. | The apertures are 12 mil in diameter with 20 mil pitch. | We are using Alpha Metals WS-609 paste. | | Any suggestions would be greatly appreciated. | | Thanks, | Doug | Doug: I'm not sure, this might give you a sense of perspective:

Pkg Ptch Aprtr Thick Aspect Area Ease

uBGA 30 11sqr 5 2.2 0.6 Hard, like 16 pitch QFP uBGA 30 13sqr 5 2.6 0.7 Kind hard, like between 20 and 16 pitch

where: dimensions are mils aspect=aperture width/foil thick SB GT 1.2 for laser cut Area ratio = (LxW)/(2x(L+W)xT) SB GT 0.66

Good luck

Dave F

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| I've had some trouble pasting a test board for a MicroBGA trial. Most of the paste remains in the stencil apertures. | The stencil is 6 mil thick, laser cut and electo-polished. | The apertures are 12 mil in diameter with 20 mil pitch. | We are using Alpha Metals WS-609 paste. | | Any suggestions would be greatly appreciated. | | Thanks, | Doug | Doug: One more (at this time) thing, WS 609 is a Type 3 paste. You might talk with your solder paste techical type and see if maybe a Type 4 might not be better suited for you. Ta. Dave F

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| I've had some trouble pasting a test board for a MicroBGA trial. Most of the paste remains in the stencil apertures. | The stencil is 6 mil thick, laser cut and electo-polished. | The apertures are 12 mil in diameter with 20 mil pitch. | We are using Alpha Metals WS-609 paste. | | Any suggestions would be greatly appreciated. | | Thanks, | Doug |

Using the same paste and having square apertures instead of round ones and of course metal blade. Should help a lot.

And if you could also use .005thk stencil instead of .006thk. The final volume of paste will only increase by about 5% by joint. And that will work very well for you combined with the sq. apertures.

Mario

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| I've had some trouble pasting a test board for a MicroBGA trial. Most of the paste remains in the stencil apertures. | The stencil is 6 mil thick, laser cut and electo-polished. | The apertures are 12 mil in diameter with 20 mil pitch. | We are using Alpha Metals WS-609 paste. | | Any suggestions would be greatly appreciated. | | Thanks, | Doug | Doug - Try 12 mil square apertures with about 2-3 mil corner radius. We have a test stencil with both circles and squares, and the difference in printing is dramatic. Regards.

Glenn Robertson

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| | I've had some trouble pasting a test board for a MicroBGA trial. Most of the paste remains in the stencil apertures. | | The stencil is 6 mil thick, laser cut and electo-polished. | | The apertures are 12 mil in diameter with 20 mil pitch. | | We are using Alpha Metals WS-609 paste. | | | | Any suggestions would be greatly appreciated. | | | | Thanks, | | Doug | | | Much of the work we've done with 20 mil pitch devices is done with nearer 1:1 aperture to pad relationships. When using no-clean types, as you might be suggesting, the paste can be especially "sticky" requiring larger openings to effect required prints thus violating some reduction rules for other device types. Also, more frequent stencil cleaning, in the machine, is required - every two prints with wet, dry, vacuum programming, as an example. | | Earl Moon | You could try an old fashioned chem etched stencil with a trapizoidal apeture and electropolishing for better release. Smaller solder balls in your paste, too. The rounded sidewalls in chem etch combined with smaller solder balls help to prevent solder packing in the corners of the apetures that will inhibit release. Some laser cut stencils in smaller diameter apetures are actually cutting facited or angular openings allowing for corners to form. Small defect I admit, but you can never tell. GoodLuck...Dan.

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| | | I've had some trouble pasting a test board for a MicroBGA trial. Most of the paste remains in the stencil apertures. | | | The stencil is 6 mil thick, laser cut and electo-polished. | | | The apertures are 12 mil in diameter with 20 mil pitch. | | | We are using Alpha Metals WS-609 paste. | | | | | | Any suggestions would be greatly appreciated. | | | | | | Thanks, | | | Doug | | | | | Much of the work we've done with 20 mil pitch devices is done with nearer 1:1 aperture to pad relationships. When using no-clean types, as you might be suggesting, the paste can be especially "sticky" requiring larger openings to effect required prints thus violating some reduction rules for other device types. Also, more frequent stencil cleaning, in the machine, is required - every two prints with wet, dry, vacuum programming, as an example. | | | | Earl Moon | | | You could try an old fashioned chem etched stencil with a trapizoidal apeture and electropolishing for better release. Smaller solder balls in your paste, too. The rounded sidewalls in chem etch combined with smaller solder balls help to prevent solder packing in the corners of the apetures that will inhibit release. Some laser cut stencils in smaller diameter apetures are actually cutting facited or angular openings allowing for corners to form. Small defect I admit, but you can never tell. | GoodLuck...Dan. | | Dan, I too go with the chem milled types and find them very useable as you said with trap cuts and polishing.

Earl Moon

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